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You are here: Home / Python / itertools / itertools.repeat / 3 Ways To Create a List Repeating an Item

3 Ways To Create a List Repeating an Item

December 16, 2018 by cmdlinetips

Sometimes, you may want to create a list in Python such that it contains the same element repeated many times. In Python, you can create such a repeat list easily using many approaches.

Here are three ways one can create a list with a single element repeated ‘n’ times.

1. How to Create a Repeat List with List Comprehension?

One way to create a list with same elements repeated is to use list comprehension. For example, if we want to create a list of size 10 with a single element ‘a’, we can use list comprehension as follows

>['a' for i in range(10)]
['a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a']

2. How to Create a Repeat List with itertools?

Python module itertools has a function called repeat, which can be used to get a list repeating single element n times. If we want to create a list repeating number 5, ten times we can use itertools.repeat function as follows

import itertools
itertools.repeat(5, 10)

itertools.repeat function yields an iterator not a list. So to get a list we can convert the iterator using list function. One of the biggest benefits of itertools.repeat is that it defers the computation until it is needed, so suitable for creating a large iterator/list.

>list(itertools.repeat(5, 10))
[5, 5, 5, 5, 5, 5, 5, 5, 5, 5]

3. How to Create a Repeat List  Simplest Way??

Third way to create a list repeating the same element is to use the * operator. We should create a list with the iter that we want to create and use the * operator to get the repeat list as follows.

>['a'] * 10
['a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a', 'a']

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Filed Under: itertools.repeat, Python Create List repeating elements Tagged With: create repeat list, itertools.repeat

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